#include <iostream>
#include <vector>

using namespace std;

class Solution
{
public:
    int combinationSum4(vector<int>& nums, int target)
    {
        vector<double> dp(target + 1);
        dp[0] = 1;
        for (int i = 1; i <= target; i++)
            for (auto x : nums)
                if (i >= x)
                    dp[i] += dp[i - x];
        return dp[target];
    }
};

int main()
{
    vector<int> v{ 1,2,3 };
    cout << Solution().combinationSum4(v, 4) << endl;

    return 0;
}